1. Field of the Invention
The present invention is in the field of metallization of semiconductor components particularly thyristors whose conductive patterns are provided by selective use of photoresist compositions and in which a multi-plane series of layers is provided permitting selective etching through the layers depending on the choice of solvent.
2. Description of the Prior Art
Because of high current load, power semiconductor components must be provided with relatively large connector structures. For this purpose, particularly in the case of disconnectable thyristors or in the case of finger type structures, the metal layer constituting the emitter circuit must have a greater thickness, for example, 20 .mu.m, than the thickness of the base metal layer which is typically about 5 .mu.m.
It has previously been proposed to manufacture a two-level-metallic structure wherein a groove or channel is etched and a simple metallizing procedure is conducted, or by employing round sections of molybdenum or silver on the electrode surfaces. Other possibilities include the use of two etching processes in sequence, or reinforcing one of the two contacts. These methods are relatively costly and imprecise.
A method for the manufacture of an auxiliary emitter electrode, and emitter electrodes of a thyristor, is disclosed in German Letters Patent No. 24 31 506 (U.S. Pat. No. 4,096,623). The disclosure of said U.S. Patent is incorporated herein by reference. In this known method, the semiconductor base member of the thyristor is covered with a metal layer having a thickness appropriate for the emitter electrodes. By means of a first photomasking operation, a first pattern consisting of a first photosensitive resist is applied in a configuration of the emitter electrode and the control electrode. By means of a second photomasking, a second pattern corresponding to the configuration of the auxiliary emitter electrode is applied, consisting of another photosensitive resist whose solvent does not dissolve the first photosensitive resist. Subsequently, through a first etching, the unmasked regions of the metal layer are etched away, the second pattern is separated and the auxiliary emitter electrode is brought by means of a second etching to the desired thickness. The metallization layer consists of aluminum, the first resist layer consists of a negative reacting resist composition, and the second resist layer utilizes a positive acting resist layer.
The method described in this aforementioned patent, which operates with two different photoresists, possesses the great advantage of employing a photoresist structure only on planar layers, that is, edge covering problems do not occur in the case of 20 .mu.m high metal layers. However, difficulties arise due to the fact that a uniform etching of a 5 to 15 .mu.m-thickness of aluminum layer is not readily attainable over a larger area such as a diameter of 50 to 100 mm.